1. Field of the Invention
The present invention relates to a system and method for controlling a variable geometry diffuser, and more specifically to controlling the diffuser to minimize noise, without adversely affecting performance.
2. Description of the Related Art
Conventional compressors used in chiller systems may be operated over a broad range of capacities in order to meet the load requirements. Typically, a chiller system is designed to keep the chilled water produced by the chiller at a preselected temperature, or temperature range. As the cooling load varies, it is necessary to vary the capacity of the compressor, in order to keep the chilled water at the preselected temperature.
As the capacity of a compressor varies, the noise generated by the compressor will also vary, particularly if no other changes in the compressor operation are made. In addition, as capacity varies, it is necessary to stabilize the fluid flow through the compressor. Unstable flow creates turbulence which causes vibration and a decrease in efficiency and which in the extreme can cause surge which is a complete reversal of the flow. If left uncorrected, surge will cause damage to the compressor.
In order to increase the stability of fluid flow in the compressor, compressors have been developed which are capable of varying the geometry of the diffuser. For example, U.S. Pat. No. 4,527,949 to Kirtland, U.S. Pat. No. 416,583 to Byrns, and U.S. Pat. No. 3,032,259 to Jassniker disclose variable geometry diffusers. Such devices require a system to control the varying geometry of the diffuser so as to increase the stability of the flow. Such control systems are generally designed to maintain compressor operator at a specific level of stability or efficiency. For example, U.S. Pat. No. 4,503,684 to Mount et al. discloses a control system which maintains flow as close to the point of surge as possible in order to maximize efficiency.
Although methods and systems have been developed to prevent surge or maximize efficiency, to the inventors' knowledge, no methods have been developed to minimize the noise produced by a chiller system having a variable geometry compressor, while still providing acceptable performance. The need for a chiller system that minimizes noise has existed for a considerable time. For example, a chiller system for submarines is an example where noise minimization is critical. In addition, the reduction of noise in other commercial applications of chiller systems is also preferred. It is therefore desirable to have a method and control system for controlling a variable geometry compressor so that noise is minimized.